cgen: fix "initializer element is not constant" for const fixed arrays with struct const elements

vlib/v/gen/c/cgen.v

@@ -11944,7 +11944,16 @@ fn (mut g Gen) check_expr_is_const(expr ast.Expr) bool {
 			return g.check_expr_is_const(expr.left) && g.check_expr_is_const(expr.right)
 		}
 		ast.Ident {
-			return expr.kind == .function || g.table.final_sym(expr.obj.typ).kind != .array_fixed
+			if expr.kind == .function {
+				return true
+			}
+			// An ident naming a V const is a valid C constant expression
+			// only when that const is emitted as a simple #define'd
+			// literal (char/float/int literals). Struct, string and array
+			// consts are runtime-initialized globals, and referencing
+			// them in a static initializer produces
+			// "initializer element is not constant".
+			return expr.obj.is_simple_define_const()
 		}
 		ast.StructInit {
 			// String fields expand to the `_S()` compound literal, which strict

vlib/v/tests/consts/const_fixed_array_of_struct_const_refs_test.v

@@ -0,0 +1,43 @@
+// Regression test: a fixed-array const whose elements are references to
+// other struct consts must compile. Struct consts are runtime-initialized
+// C globals, so referencing them in a static C initializer produced
+// "initializer element is not constant"; such arrays must be initialized
+// in _vinit instead.
+struct Info {
+	code i16
+	name string
+}
+
+const first = Info{1, 'first'}
+const second = Info{2, 'second'}
+const third = Info{3, 'third'}
+
+const by_ref = [first, second, third]!
+
+// mixing references and literals must also work
+const mixed = [first, Info{9, 'literal'}]!
+
+// simple #define'd literal consts must keep working statically
+const ia = 5
+const ib = 6
+const int_refs = [ia, ib]!
+
+fn test_fixed_array_of_struct_const_refs() {
+	assert by_ref.len == 3
+	assert by_ref[0].code == 1
+	assert by_ref[1].name == 'second'
+	mut total := 0
+	for e in by_ref {
+		total += int(e.code)
+	}
+	assert total == 6
+}
+
+fn test_mixed_refs_and_literals() {
+	assert mixed[0].name == 'first'
+	assert mixed[1].code == 9
+}
+
+fn test_simple_define_consts_still_static() {
+	assert int_refs[0] + int_refs[1] == 11
+}